linux-kernel - Re: [fuse-devel] [PATCH] fuse: Fix fuse_get_user

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Message-ID: <20160420154323.GA13463@ubuntu-hedt>
Date:	Wed, 20 Apr 2016 10:43:23 -0500
From:	Seth Forshee <seth.forshee@...onical.com>
To:	Ashish Samant <ashish.samant@...cle.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	fuse-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [fuse-devel] [PATCH] fuse: Fix fuse_get_user_pages() return value

On Tue, Apr 19, 2016 at 03:57:52PM -0700, Ashish Samant wrote:
> Hi Seth,
> On 04/19/2016 03:43 PM, Seth Forshee wrote:
> >fuse_direct_io() expects this to return either 0 or a negative
> >error code, but on success it may return a positive value.
> >fuse_direct_io() may return this same value when the subsequent
> >I/O operation doesn't transfer any data, which means that it will
> >return a positive value when no bytes were transferred. This is
> >obviously problematic.
> >
> >Fix fuse_get_user_pages() to return 0 on success. This will in
> >turn make it so that fuse_direct_io() returns 0 if no bytes are
> >transferred.
> >
> >Fixes: 742f992708df ("fuse: return patrial success from fuse_direct_io()")
> >Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
> >---
> >  fs/fuse/file.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> >index b5c616c5ec98..78af5c0996b8 100644
> >--- a/fs/fuse/file.c
> >+++ b/fs/fuse/file.c
> >@@ -1295,7 +1295,7 @@ static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
> >  	*nbytesp = nbytes;
> >-	return ret;
> >+	return ret < 0 ? ret : 0;
> >  }
> >  static inline int fuse_iter_npages(const struct iov_iter *ii_p)
> 
> 
> I have already sent a patch to the list that does exactly the same thing :)
> 
> https://sourceforge.net/p/fuse/mailman/message/34966327/

Oops, should have checked the list first I guess :-)

But that's from several weeks ago, and it's still not applied? This is
causing big problems for lxcfs on 4.6-rc kernels, so it's definitely a
regression and needs to get fixed.

Thanks,
Seth